1. Field of the Invention
The instant invention relates to a discharge electrode utilizing an electron-emitting layer, and a discharge lamp utilizing the discharge electrode.
2. Description of the Related Art
Discharge lamps have been widely used as a general use light source, an industrial light source, and various integrative light sources. Above all, a low voltage discharge lamp such as a fluorescent lamp has a big market dominating approximately half of the illuminative light source market. With these discharge lamps including the fluorescent lamp that form a big market, recent demands for resource saving, reduction in environmental load and the like in addition to consideration for energy saving such as luminous efficiency have been increasing. In regards to energy saving, obtaining higher luminescence intensity from the same energy is desired. There is particularly a strong market demand for cold-cathode discharge lamps for backlights and the like as they are relatively less efficient than thermal types.
Development of cathode materials is being actively conducted for resolving these issues. The search for a material that allows continuous electric discharge at a lower operating voltage than conventionally used nickel (Ni) continues, where various metals, semiconductors, and oxides are being tested. A fluorescent luminescent device employing a thermionic emission cathode, which has diamond particles provided on the surface of a cathode material such as tungsten (W), tantalum (Ta) or the like, is proposed in Japanese Patent Application Laid-open No. Hei 10-69868 and Japanese Patent Application Laid-open No. 2000-106130.
Furthermore, technology using diamond having negative or significantly smaller electron affinity than a metal electrode, graphite having sp2 bond and formed of the same carbon as the diamond, or carbon-based material having a grain boundary layer of amorphous carbon as the cold-cathode electrode is proposed in Japanese Patent Application Laid-open No. 2002-298777.
However, with the technologies disclosed in Japanese Patent Application Laid-open No. Hei 10-69868 and Japanese Patent Application Laid-open No. 2000-106130, most of the supplied electric power is consumed by the cathode material, not always showing sufficient improvement in efficiency.
Meanwhile, with the technology disclosed in Japanese Patent Application Laid-open No. 2002-298777, higher efficiency can be achieved than with the technologies disclosed in Japanese Patent Application Laid-open No. Hei 10-69868 and Japanese Patent Application Laid-open No. 2000-106130 since carbon-based electrodes having diamond layers and graphite or amorphous carbon layers are used instead of metallic electrodes made of Ni or the like, which are conventionally used as the cold-cathode electrodes. However, problems remain due to electric discharge from discharge lamps and wear-out of electrodes through sputtering due to Ar ion bombardment, resulting in a short lifetime without being able to maintain high efficiency over a long period of time.